Init local_ip and local_port properly in mg_connection

mongoose.h

@@ -37,7 +37,7 @@ struct mg_connection {
   const char *query_string;   // URL part after '?', not including '?', or NULL
 
   char remote_ip[48];         // Max IPv6 string length is 45 characters
-  const char *local_ip;       // Local IP address
+  char local_ip[48];          // Local IP address
   unsigned short remote_port; // Client's port
   unsigned short local_port;  // Local port number